Magnetically shielded cutout for electric motors



T. s. TAYLOR 2,199,232 MAGNETICALLY SHIELDED CUTOUT FOR ELECTRIC MOTORS April 30, 1940.

File i Dec. 11, 1951 Patented Apr. 30, 1940 UNITED STATES PATENT OFFICE MAGNETICALLY SHIELDED CUTOUT FOR ELECTRIC MOTORS Application December 11, 1932, Serial No. 179,235

4 Claims.

This invention relates to electric motors, more particularly of the single-phase induction type having a main exciting winding and a starting winding with a speed-responsive switch or cutout to open the circuit through the starting winding when the motor comes up to speed.

Speed-responsive cutouts for motors of the type in question commonly employ a weighted member which is biased by one or more springs in a direction opposite to the direction in which it tends to move under centrifugal force. For reliable operation, the cutout biasing spring or springs must be calibrated and must be made of a material which will retain a constant resiliency over long periods of use. Steel springs are found to be suitable for the purpose but are often found to be affected by stray magnetic fields in the motor causing them to vibrate noisily.

The present invention therefore has for an object to provide an induction motor with a speedresponsive cutout which is free from vibrating spring noise.

With the above and other objects in view, as will hereinafter appear, the invention comprises the devices, combinations, and arrangements of parts hereinafter set forth and illustrated in the accompanying drawing of a preferred embodiment of theinvention, from which theseveral features of the invention and the advantages attained thereby will be readily understood by those skilled in the art.

In the accompanying drawing, Fig. 1 is an axial section of an induction motor embodying the invention. Fig. 2 is a similar section through the rotor of the motor taken in a plane from the plane of the section shown in Fig. 1. Fig. 3 is a section on the line 3-3,-Fig. 1. Fig. 4 is an internal face view of the cutout switch device. Fig. 5 is a top edge view of the switch device. Fig. 6 is a section on the line 6-6, Fig. 4. Fig. 7 is a section on the line 1-4, Fig. 4, and Fig. 8 is a diagrammatic representation of the motor.

The motor has a frame including the lam-v inated statorcore I to which is clamped endbonnets, one of which is shown at 2, having bearings 3 for the shaft 4 of the rotor body 5 supporting the integrally cast aluminum bars 6 and end-rings 1 of the conventional squirrelcage secondary winding. The stator l carries the conventional main and starting windings M and S of the conventional split-phase motor indicated in Fig. 8.

Thecutout C for the starting winding pref- "erably comprises a polded base 8 of insulating tion to open the switch contacts i3, ll.

tail IQ of the lever il engages a stop-surface 22 material having holes 9 in which are riveted the I pivot hooks I 0 for the sheet-metal levers II and I2. The lever II is the actuating lever whereas the lever. I2 is the actuated lever and carries the movable contact i3 which at times, engages the stationary contact I on the terminal plate 15. A toggle thrust-member comprising a bar It and compression coil-spring I! are interposed between the levers H and I2. The toggle thrustmember insures a snap action or quick make and break of the switch contacts and works on the same principle as that disclosed in the U. S. patent of J. M. Naul, No. 2,083,343, dated June 8, 1937.

A recovery spring i8 is interposed between the base 8 and lever ii to bias the latter in a direc- The on the base 8 to limit the motion of the lever H under the influence of the spring It. The lever ll carries two felt pads 2| for rubbing engagement by the collar 22 of molded insulating material which is siidable on and endwise of the shaft I.

The collar 22 is engaged by the inturned arms 23 of the weighted levers 24 fulcrumed at 25 in the spaced parallel ears 26 of a sheet-metal frame 2! preferably of ferrous metal which is fixed to the motor shaft l closely adjacent the aluminum end-ring i of the rotor 5.

A pair of calibrated steel coil-springs 22, 28 connect the weighted levers 2!, 2l together and yieldingly draw them toward the shaft 4, thereby causing the arms 23, 23 to force the collar 22 against the felt pads 2i and shift the switch lever ii in a direction to close the switch contacts l3, It; the springs 28 being strong enough to overcome the resistance of the spring l8. The springs 28 closely overlie the end-rings T, as shown in Figs. 2 and 3.

It has been found that the construction above described is noisy in operation and careful investigation and study have revealed that the noise is caused by lateral vibration of the springs 28 in the stray magnetic field adjacent the rotor end-rings I. This noise has been eliminated by interposing between the end-ring I and springs 28 a thin sheet-metal plate 29 of magnetic metal such as sheet-iron having ends 36. bent at right angles to the plane of the plate 29 so as to partially surround the springs 28. The plate 29 "may be spot-welded at 3| to the frame 21. This plate 29 with its angularly bent ends 30 constitutes a magnetic shield for the springs 28 and eliminates noisy vibration of. the latter. Steel springs may thus be used instead of non-magnetic springs such as phosphor-bronze springs which are found not to maintain a constant calibration over a lmgth of time required for practical service. Each of the springs II lies in a trough of magnetic metal embracing three sides of the spring and constituting an effective magnetic shield for such spring.

'I'hisinvention isnot to be understood as limited to the details of construction and relative arrang'ement of parts shown and described, as the foregoing disclosure is made in an illustrative sense and not in limitation of the invention, the scope of which is indicated by the appended claims.

Having thus set forth the nature of the invention, what I claim herein is:

1. In an alternating current motor, a stator having an exciting winding, a rotor body disposed within the field of said stator, a rotor shaft, a speed-responsive device mounted on the rotor shaft and including a coil spring-biased weighted member, a sheet-iron magnetic shield interposed between said rotor body and said spring, and motor starting means governed by said speedresponsive device, said shield having an end-portion bent to stand in a plane at an angle to the plane of the shield proper and paralleling the axis of said spring.

2. In an alternating current motor, a stator having an exciting winding, a rotor body disposed within the field of said stator, a rotor shaft, a speed-responsive device mounted on the rotor shaft and including a pair of weighted levers, a pair of coiled steel tension-springs connecting said levers, a sheet-iron magnetic shield presenting spaced troughs each containing a respective one of said springs and disposed between said prings and the rotor body, and a cutout switch under the control of said speed-responsive device.

3. In an alternating current motor, a stator having an exciting winding, a squirrel cage rotor body disposed within-the field of said stator and including conductor bars and connecting end rings, a rotor shaft, a speed-responsive device mounted on the rotor shaft and including a coilspring-biased weighted member, a trough-shaped shield of magnetic metal containing said coilpring and disposed between the latter and the adjacent end ring of said rotor body, and motor starting means governed by said speed-responsive device.

4. In an alternating current motor, a stator having an exciting winding, a squirrel cage rotor body disposed within the field of said stator, said body having conductor bars and connecting end rings, a rotor shaft, a speed-responsive device mounted on the" rotor shaft and including a frame, a weighted lever pivoted on said frame. a steel spring to bias said lever in a direction toward the rotor shaft, said spring being disposed closely adjacent one of the end rings of said rotor body and extending in a direction parallel to the adjacent face of the adjacent end ring, and a sheet of magnetic metal disposed between said spring and said adjacent end ring and having an edge portion bent to stand at anangle to the plane of said sheet proper and paralleling said THOMAS S. TAYLOR. 

